Percutaneous guidewires are commonly used in gastrointestinal, hepatobiliary and cardiac procedures. They are introduced percutaneously and manipulated through a vessel to the site of interest, using fluoroscopy, for example, to monitor the path taken by the guidewire. They are usually the first medical device that will reach the site of interest. Once in place, they can subsequently be used to reliably guide catheters, endoscopes and other delivery systems to the site of interest, by passing these delivery systems over the guidewire.
The environments in which percutaneous guidewires must operate tend to place conflicting constraints on their design. For instance, the guidewire must typically have sufficient stiffness to enable a physician to pass them along the vessel they are introduced through, as well as to accurately guide the delivery systems that they are subsequently employed to deliver. On the other hand, they need to be flexible enough to follow the sometimes tortuous paths they must follow through the vasculature to reach the site of interest. An overly stiff guidewire also increases the risk of the tip of the guidewire puncturing the wall a vessel wall or other tissue it encounters.
Most modern guidewires have a composite construction consisting of a solid metal core (1) and outer metal coil (3) terminating at a rounded, atraumatic tip (4), as illustrated schematically in FIG. 1. At a distal end portion (2) of the guidewire, the inner core tends to be ground or drawn so that its diameter reduces towards to the tip of the guidewire. This reduces the stiffness of the distal end portion of the guidewire to reduce the risk of the wire end puncturing soft tissue.
A majority of guidewires are supplied straight, although many are provided with a tip portion that can be manually bent into a desired shape by the user, for example to aid in navigating a tortuous path. In some case the user may bend the end of the wire to help minimise the likelihood that the wire end causes trauma if it impinges on soft tissue; on impact, force is transmitted radially rather than longitudinally along the wire.
More recently, it has been proposed to manufacture guidewires with a pre-formed curve at their distal end portion (2), as seen schematically in FIGS. 2a and 2b. The curved form of the end of these so called ‘J-tip’ guidewires further reduces the likelihood of trauma if the end of the wire impacts soft tissue as it is being advanced.
One area of increasing importance for the use of guidewires is in coronary interventions and, more recently, structural interventions of the heart, in particular percutaneous heart valve (PHV) placement. When implanting a PHV at the aortic position a guidewire (5) is first fed into the left ventricle (7) of the heart (6), as illustrated in FIG. 3. This wire in then used to guide the PHV into position, typically involving iterative pushing and pulling of the guide wire before the artificial valve is seated in the correct position.
The demands placed on a guidewire by this particular application are great and are at (or in some cases beyond) the limit of current devices.
More specifically, in order to successfully place the artificial valve the wire must be stiff enough at the aortic valve to sufficiently support the delivery system. However, the tip must be atraumatic enough to prevent damaging the thin ventricular wall should it come into contact during the pushing and pulling of the valve delivery.
Typically a straight guidewire is used for this. The guide wire may, however, have a user imparted bend to help it conform to the V shape of the ventricle (as shown in FIG. 3a). Even then there is still a high risk, especially if the user has imparted a bend to the wire with a small radius of curvature, that if the wire contacts the ventricular wall it will kink and potentially cause traumatic injury (see FIG. 3b).